High-fiber, nutrient-dense foods such as soybeans, kale, and broccoli in a balanced diet do not adversely affect people with normal thyroid function.
The thyroid produces hormones to help regulate your body’s metabolism and calcium levels. Goitrogens found in wheat gluten, soybeans, and vegetables such as kale, broccoli, and Brussels sprouts get a bad rap because they can block some iodine absorption and may interfere with thyroid function. Iodine deficiency is not a major concern as the American diet provides adequate amounts, often through table salt.
A clinical review (1) found that people with healthy thyroid function who ate soy were not at increased risk for thyroid problems. Findings of the Cancer Prevention Institute of California’s Bay Area Thyroid Cancer Study (2) found that women who consumed the most soyfoods, both traditional and modern, have about half the risk of thyroid cancer compared to those who consumed the least.
1. Messina M, Redmond G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid. 2006;16:249-258.
2. Horn-Ross PL, Hoggatt KJ, Lee MM. Phytoestrogens and thyroid cancer risk: the San Francisco Bay Area thyroid cancer study. Cancer Epidemiol Biomarkers Prev. 2002 Jan;11(1):43-9.